having wayyy tooo much trouble with this simple assignment.

Question

Is there a lab that proves that the light reactions must occur prior to the dark reactions in photosynthesis?

So far, I thought of the experiment in which one plant is placed in direct sunlight and the other is placed inside a box. The two conditions constant (i.e. same type of plant, same amounts of water) apart from the lack of sunlight received by the second plant in the box. But would this experiment really prove that the light reactions occur first?? And if so, would weighing the mass of the plants indicate the information necessary to show that light reactions must occur first?